Method of adjusting tension applied to sheet, and device for the same

Abstract

To prevent disalignment of the edges of a folded sheet by smoothly feeding the sheet to a packaging unit while keeping tension fluctuations to a minimum when the sheet is unwound from a paper roll set in a paper feed unit even though the paper roll diameter decreases gradually as the sheet is unwound. A sheet length measuring sensor or rotary encoder is provided in the paper feed path through which the packaging sheet is fed toward the packaging unit. An angle sensor is provided which includes Hall element sensors provided on a support shaft and magnets provided on a core pipe of the paper roll. Any change in the signals from one of these sensors relative to the signal from the other sensor is used to calculate the paper roll winding length, and the sheet tension is adjusted to an optimum, constant level by controlling the sheet braking force stepwise according to the roll diameter measured by the sensors.

What is claimed is: 
     
       1. A roll sheet assembly for use with a drug packaging device including a sheet feed unit comprising a fixed shaft, a first rotary shaft rotatably mounted around the fixed shaft and carrying said roll of sheet material, a first brake means for applying a braking force to the first rotary shaft, and feed rollers for feeding the sheet material from said roll, a second brake means for producing a constant braking force between the first rotary shaft and said roll of sheet material, a packaging unit comprising a triangular plate for folding the sheet material in half so as to form a valley in the sheet material, a hopper for dropping drugs into the valley formed in the sheet, and heating rollers for heat-sealing the sheet material in a width direction at predetermined intervals and along top edges thereof to form a plurality of bags with the drugs sealed therein,
 the sheet feed unit further comprising a sheet length sensor for measuring a feed length of the sheet in a sheet feed path leading to the packaging unit, a first angle sensor for detecting a rotation angle of said roll of sheet material, and a control unit for calculating a current sheet length on said roll of sheet material and the diameter of said roll of sheet material based on the sheet length measured by the sheet length sensor and the rotation angle measured by the angle sensor, and controlling a direct-current voltage applied to the first brake means,   said roll sheet assembly comprising a cylindrical second rotary shaft having a cylindrical outer periphery and a cylindrical inner periphery, sheet material wound on said cylindrical outer periphery of said second rotary shaft, and at least one magnet provided on said cylindrical inner periphery of said second rotary shaft.   
     
     
       2. The roll sheet assembly as claimed in claim  1  4, wherein said at least one magnet comprises four magnets circumferentially spaced at equal intervals. 
     
     
       3. The roll sheet assembly as claimed in claim  1  4, wherein said at least one magnet is detachably mounted on said inner cylindrical periphery of said second rotary shaft. 
     
     
       4. An assembly for use with a drug packaging device provided with a sheet tension adjusting device, said drug packaging device comprising a sheet feed unit and a packaging unit,
 the sheet feed unit comprising: a fixed shaft, a first rotary shaft rotatably mounted around the fixed shaft, and a first brake means for applying a braking force to the first rotary shaft;   the assembly comprising: a cylindrical second rotary shaft having a cylindrical outer periphery and a cylindrical inner periphery, a roll of sheet material wound on said cylindrical outer periphery of said second rotary shaft, and at least one magnet provided on said cylindrical inner periphery of said second rotary shaft;   the packaging unit comprising: a sealing portion for heat-sealing said sheet material in a width direction at predetermined intervals and longitudinally to form a plurality of bags with drugs sealed therein; and   the sheet feed unit further comprising: feed rollers for feeding the sheet material from said roll of sheet material; a second brake means for producing a constant braking force between the first rotary shaft and said roll of sheet material; an angle sensor for detecting a rotation angle of said second rotary shaft; a sheet length sensor for measuring a feed length of the sheet material in a sheet feed path leading to the packaging unit; and a control unit for calculating a current sheet length on said roll of sheet material and the diameter of said roll of sheet material based on the sheet length measured by the sheet length sensor and the rotation angle measured by the angle sensor, and controlling a direct-current voltage applied to the first brake means.   
     
     
       5. An assembly for use with a drug packaging device provided with a sheet tension adjusting device, said drug packaging device comprising a sheet feed unit and a packaging unit, the sheet feed unit comprising:
 a fixed shaft;   a first rotary shaft rotatably mounted around said fixed shaft; and   a first brake means for applying a braking force to said first rotary shaft;   the assembly comprising: a cylindrical second rotary shaft having a cylindrical outer periphery and a cylindrical inner periphery, a roll of sheet material wound around said cylindrical outer periphery of said second rotary shaft, and at least one magnet provided on said cylindrical inner periphery of said second rotary shaft;   the packaging unit comprising; a sealing portion for heat-sealing said sheet material in a width direction at predetermined intervals and longitudinally to form a plurality of bags with drugs sealed therein; and   the sheet feed unit further comprising:   feed rollers for feeding the sheet material from said roll of sheet material;   a second brake means for producing a constant braking force between the first rotary shaft and said roll of sheet material;   a first angle sensor for detecting a rotation angle of said second rotary shaft;   a sheet length sensor for measuring a feed length of the sheet material in a sheet feed path leading to said packaging unit;   a control unit for calculating a current sheet length on said roll of sheet material and the diameter of said roll of sheet material based on the sheet length measured by said sheet length sensor and the rotation angle measured by said first angle sensor, and controlling a direct-current voltage applied to said first brake means; and   a second angle sensor for detecting a rotation angle of said first rotary shaft, wherein if signals from said first and second angle sensors do not coincide, said first rotary shaft and said second rotary shaft are judged rotating relative to each other, so that tension is relaxed by controlling a direct-current voltage applied to said first brake means.   
     
     
       6. The assembly of claim 5, wherein said at least one magnet comprises four magnets circumferentially spaced at equal intervals. 
     
     
       7. The assembly of claim 5, wherein said at least one magnet is detachably mounted on the cylindrical inner periphery of said second rotary shaft.